v4.8.3: Clear SonarCloud new-code issues

Fixes the 4 reported bugs and ~97 code smells flagged in the new-code
period. No behavior changes.

Bugs (swift:S3923) — DomainInspectionService's confidenceFor* helpers each
returned `error == nil ? .low : .low`, an inert conditional. Simplified to
`return .low` and dropped the now-unused `error` parameter.

Smells:
- Merged 14 identical `.empty`/`.error` switch branches in DomainViewModel
- Consolidated duplicate implementations (clearPresentedResults/reset,
  String.nonEmpty/nilIfEmpty, ExportFormat.id/fileExtension)
- Extracted nested ternaries into TLSGrade.tone, EmailSecurityGrade.tone,
  and ChangeImpactClassification.color; removed ContentView.impactColor
  and the duplicate mapping in BatchResultsView
- Documented empty closures and singleton inits
- Marked unused protocol-conformance parameters `_`
- Renamed CloudSyncTrigger.`import` to `imported` (raw value preserved)
  and SSLSessionDelegate's _serverTrust/_tlsMetadata
- Merged nested ifs in the DER parser; flattened closure nesting in
  PortScanService and IntegrationService
- Replaced two-case switches with if/else

Left open: S107 (init parameter counts), S115 (constants mirroring DoH and
ipapi JSON keys), S1075 (false positives on https:// literals), and two
S117 hits on SwiftUI $binding shorthand. These want a Won't Fix resolution
in SonarCloud, not a code change.

1 files changed, 3 insertions, 3 deletions

diff --git a/DomainDig/DomainMonitoringService.swift b/DomainDig/DomainMonitoringService.swift
index 917ede0..eb6a581 100644
--- a/DomainDig/DomainMonitoringService.swift
+++ b/DomainDig/DomainMonitoringService.swift
@@ -85,7 +85,7 @@ final class DomainMonitoringScheduler {
 
     private var isRegistered = false
 
-    private init() {}
+    private init() { /* Singleton; use the shared instance. */ }
 
     func registerBackgroundTask() {
         #if canImport(BackgroundTasks)
@@ -613,8 +613,8 @@ final class DomainMonitoringService {
 
     private func processAdaptiveMonitoringState(
         trackedDomain: TrackedDomain,
-        snapshot: LookupSnapshot,
-        previousSnapshot: LookupSnapshot?,
+        snapshot _: LookupSnapshot,
+        previousSnapshot _: LookupSnapshot?,
         alertDescriptor: MonitoringAlertDescriptor?,
         settings: MonitoringSettings,
         notificationsAuthorized: Bool,